1. Field of the Invention
The present invention relates to a method used for an induction type power supply system, and more particularly, to a method capable of detecting whether an intruding metal exists in a power transmission region of an induction type power supply system.
2. Description of the Prior Art
In an induction type power supply system, a power supply device applies a driver circuit to drive a supplying-end coil to generate resonance, in order to send electromagnetic waves. A coil of the power receiving device may receive the electromagnetic waves and perform power conversion to generate DC power to be supplied for the device in the power receiving end. In general, both sides of the coil are capable of transmitting and receiving electromagnetic waves; hence, a magnetic material is always disposed on the non-induction side of the coil, allowing the electromagnetic energy to be aggregated on the induction side. The magnetic material close to the coil may enlarge the coil inductance, which further increases the electromagnetic induction capability. In addition, the electromagnetic energy exerted on a metal may heat the metal; this principle is similar to an induction cooker. Therefore, another function of the magnetic material is to isolate the electromagnetic energy, in order to prevent the electromagnetic energy from interfering the operations of the device behind the coil, and also prevent the electromagnetic energy from heating surrounding metals for safety.
The induction type power supply system includes a power supply terminal and a power receiving terminal, where an induction coil is included in each terminal for sending power energy and control signals. The safety issue should be considered in this system. However, a user may intentionally or unintentionally insert a metal between these induction coils when using the induction type power supply system. If an intruding metal appears during power transmission, the electromagnetic energy generated by the coil may rapidly heat the intruding metal and cause an accident such as burning or exploding. Therefore, the industry pays much attention to this safety issue, and related products should possess the capability of detecting whether an intruding metal exists. When there exists an intruding metal, power supply output should be cut off for protection.
The prior art (U.S. Publication No. 2011/0196544 A1) provides a method of detecting whether an intruding metal exists between the power supply terminal and the power receiving terminal. This method has been applied to the products on sale. However, the prior art still possesses at least the following shortcomings:
First, the prior art calculates a power loss by measuring an output power of the power supply terminal and an input power of the power receiving terminal, and determines existence of the intruding metal based on the calculated power loss and a predetermined threshold value. If the power loss exceeds the threshold value, an intruding metal is determined to exist. The maximum problem of the method is in the configuration of the threshold value. If the threshold limit is too strict, the system may wrongly determine that there is an intruding metal under a normal operation; if the threshold limit is too loose, the protection may not be triggered when some types of intruding metals exist. For example, when a smaller intruding metal such as a coin, key or paper clip exists in the power transmission region of the power supply terminal, there may not appear an evident power loss but the intruding metal may still be heated significantly. Further, the configuration of the threshold value should be determined by performing data analysis based on a large number of physical samples; this consumes a lot of time and efforts.
Second, in the induction type power supply system, the factors affecting the power transmission loss between the power supply terminal and the power receiving terminal are very complex. The power loss may be affected by various events such as functionalities of circuit elements, matching of the coil and the magnetic material, relative distance and horizontal location offsets of the coils in both terminals, and media characteristics between the coils, e.g., metal paints on the coils. Since there are numerous affecting factors, the power losses of the products due to element offsets are different. Therefore, the threshold value cannot be too severe, which results in a limited protection effect.
Third, in the industry associated with the induction type power supply system, the power supply terminal and power receiving terminal of an induction type power supply system may be manufactured by different manufacturers and/or in different periods based on commercial circulation. The configuration of the above threshold value is usually implemented in the power supply terminal, but the related power setting should be adjusted for various types of power receiving circuits. It is hard to fully consider the characteristics of every type of power receiving circuits, such that compatibility problems are unavoidable.
Fourth, a circuit for implementing power measurements should be disposed in each of the power supply terminal and power receiving terminal, and the related circuit cost is necessary. In order to perform power measurements with high accuracy, the implementation requires a more complex circuit and thus requires a higher cost. The difficulty of the implementation is also higher.
Fifth, different power settings may possess different power losses. For example, an induction type power supply system has an output power equal to 5 watts (W). Assuming that its basic power loss substantially ranges from 0.5 W to 1 W, the power loss generated by the intruding metal may not be detected if the power loss is within 1 W. If the output power is increased to 50 W, the basic power loss will significantly increase to a range between 5 W and 10 W with the same circuit design. The power threshold for determining the intruding metal should also be increased with the same ratio. In such a condition, many types of intruding metals may not be detected. For example, the power loss generated by a paper clip is quite small, and is easily ignored by the conventional intruding metal detection method, while the electromagnetic induction energy received by the paper clip is still large enough to generate high temperature and cause an accident. In other words, the conventional intruding metal detection method is not feasible when the induction type power supply system is supplying power, especially when the supplied power is high.
Thus, there is a need to provide another method of detecting the intruding metal, in order to improve the protection effects on the induction type power supply system.